Phytase is an enzyme, which breaks down phytate to inositol and orthophosphoric acid. Phytate is the major phosphorus source in plants and plays an important role during germination for ATP synthesis. However, six reactive groups of phytate make it a poly anionic chelating agent, which reacts with proteins, amino acids, and divalent cations. Therefore, phytate consumption may cause bone weaknesses, tooth decays, iron deficiencies, and general malnutrition. In addition, while ruminant animals sustain the microflora, which breaks down phytate; monogastric animals such as chickens and pigs can produce little or no phytase in their intestine. Since, monogastric animals are generally fed with soybean and other meals, which have a high concentration of phytate, excessive phosphorus accumulation occurs in their manure. This causes problems such as water pollution, algal blooms, fish kills, and changing of fauna and flora in the environment. In order to solve these problems, supplementing diets with phytase as the feed additive is getting attention in the food and feed industry. To date, phytase production has been usually performed as a solid-state fermentation with small production volumes. Therefore, the aim of this study was to increase the phytase activity in submerged fermentations by screening several microorganism strains based on the literature to select the most productive phytase producer and optimizing growth parameters such as temperature, pH, and aeration level using response surface methodology (RSM). As a result, among the four different microorganisms evaluated, Aspergillus ficuum (NRRL 3135) was selected as the most productive strain. Optimum temperature, pH, and aeration values were determined as 33°C, pH 4.5, and 0.9 vvm, respectively, for A. ficuum in 2-L batch submerged phytase productions. Under these conditions, phytase activity was measured as 2.27 U/ml, which is 2 folds higher than shake-flask fermentations. Therefore, this is a unique study showing the production of phytase with A. ficuum successfully in submerged fermentation as opposed to the traditional solid-state fermentation.